1. Field of the Invention
This invention generally relates to mechanical tools, and more particularly to a tool for pulling nails from cylindrical stakes.
2. Description of the Prior Art
Stakes are used extensively in the concrete construction trade. The stakes are commonly cylindrical in shape and made from metal, although other materials like wood or plastic may be used. When concrete is poured, it is in a semi-liquid state and forms are required to constrain the concrete to a desired boundary. The stakes, which are driven into the ground with a sledgehammer, have pre-drilled holes passing through their body at a right angle to their central axis. It is the job of the workman when he drives the stake in the ground to orient the stake so that the pre-drilled holes are at right angles to the form. The form, is often a 2xe2x80x3xc3x976xe2x80x3 wooden plank. A nail, whose shank is of a smaller diameter than the pre-drilled hole in the stake and may utilize two heads on one end, is inserted into a hole in the stake and then driven into the form board. Nailing the form boards to the stakes ensures that the forms are held firmly in place while the concrete dries.
Once the concrete has hardened, the stakes must be pulled from the ground and the forms removed so finishing work may commence. Before this can happen, however, the nails securing the forms to the stakes must be removed. The currently-available tools, however, make such nail removal a very clumsy and time consuming task, primarily because of two factors. First, the close proximity of the nail to the ground limits the tool""s operational space and its orientation to the stake. Second, it is difficult to locate and support a fulcrum point on a cylindrical stake.
A search for prior art found several examples of nail pulling implements. One example is U.S. Pat. No. 6,257,553 to Khachatoorian, dated Jul. 10, 2001, which depicts a device that relies on a fulcrum and lever arm to provide a mechanical advantage for easier nail extraction. This device, however, like the common claw hammer, which operates on a similar principle, does not lend itself well to removing nails from concrete form stakes due to the factors cited in the preceding paragraph. If the device is aligned parallel with the stake centerline during use, then, depending on whether the handle is located below or above the engaged nail, either the handle or the claw that grips the nail will likely come into contact with the ground. This is especially true of the claw hammer which seems to be the tool of choice in the large majority of cases. Thus, the ground would hinder the device""s room to operate and impede its ability to remove the nail. If the nail is located close to the ground, which occurs frequently in the field due to the minimal height of the form boards, this inherent limitation of the device and of similar devices, which utilize the same fulcrum point and lever arm principle, can render the tool inoperative. Also, when the device is used in this vertical orientation, where the stake provides a suitable fulcrum point, the device is not stable and may slide off the stake if precise control is not used when operating the tool. This is because the surface of the device that contacts the stake at the fulcrum point does not match the cylindrical shape of the stake. Since contact occurs only along a thin line between the device and stake, the device lacks the ability to maintain its orientation, which to be effective must be in line with the stake central axis. If this orientation is not maintained the tool becomes unstable an often slips off the stake.
Reorienting the device so that it is parallel with the ground does not solve this problem and, in fact, introduces a different problem. Since the device is now perpendicular to the stake, the stake is unable to provide any support for the fulcrum point. Since the device cannot operate without a properly supported fulcrum point, the claw end of the tool must be rotated about the stake centerline until it comes into contact with the form board. The form board provides the required support to pull out the nail; however, when used in this manner the tool will not be able to pull the nail out straight. The nail shank will be bent around the sharp corner of the pre-drilled hole through the stake requiring extra effort by the operator of the tool. A better design would provide a well supported, stable fulcrum point by matching the cylindrical shape of the stake while eliminating the problem of interference caused by the ground and form board.
Another example of prior art is U.S. Pat. No. 5,984,272 to Crider, dated Nov. 16, 1999, which depicts a device with a slide hammer mechanism oriented inline with the nail""s central axis, that has the ability to lock onto the nail head. This device relies upon the momentum transfer between the sliding hammer and the stop on the end of the shaft to pull out the nail. The main drawback to this approach is the amount of physical effort required by the operator of the tool. Since the device does not provide any mechanical advantage, the nail extraction is limited by the physical strength and stamina of the operator. A better approach would utilize a mechanical advantage to limit the force required by the user to extract the nail Also, pulling out the nail in one smooth motion, rather than several repeated hammer strokes, would minimize the amount of energy expended by the operator of the tool.
The invention described in this document is a device for pulling nails, specifically those used to secure concrete form boards to cylindrical stakes. In one embodiment the nail pulling device is composed of a handle, or handle attachment feature, that is either attached to, or integral with a saddle having a semi-circular, concave cross section that is swept at a constant radius, thereby, forming a circular segment of approximately 60xc2x0. The stake fits inside the semi-circular, concave cross section of the circular segment, which has a radius that is slightly larger than the radius of the stake for the purpose of maintaining the alignment between the device and the stake centerline. When the device is engaged with a nail and supported by a stake, the circular segment provides the extraction force to the nail head when the handle is lifted/pushed towards the stake.
The device interfaces with the nail head via a claw groove on the end of the saddle opposite where the handle is attached. The shape of the claw groove is not the typical long tapered vee used by most existing nail puller tools, particularly the claw hammer, but is rather short, with parallel sides. In order to facilitate the entry of the nail shank into the claw groove, the open end of the groove is bell shaped. The claw groove resides in a ledge that forms the top of the claw externally and the ceiling of a pocket internally. The pocket provides clearance for the nail head closest to the stake while an appropriate ledge thickness will ensure the absence of binding between the device and the nail heads. The external surface of the ledge remains flat for a short distance from the open end of the groove before curving outward at a gentle radius. The normal distance from the contact point between the device and stake, which acts as the active fulcrum point for the handle, to the flat portion of the external surface is slightly less than the distance from the stake to the outermost nail head, to ensure that the claw fits under the outermost nail head for the purpose of extraction. The outward curve of the external surface provides support for the second nail head as the nail is extracted.
In order to pull a nail from a stake, the operator may stand facing the stake with his feet planed approximately shoulder width apart. With the stake and nail head centered in front of him, the operator holds the invention by the handle with the claw groove pointing towards the ground. Next, the operator moves the device towards the slake until the stake fits inside the concave contour of the circular segment. At this point the handle will be at an angle of approximately 60xc2x0 to the stake with the claw groove roughly a couple of inches above the nail head. The operator then slides the device down the stake so that the nail head is admitted into the claw groove. When the nail head bottoms out against the outward curving surface of the claw the operator will begin to swing the handle upwards towards the stake while maintaining a small amount of downward pressure. The downward pressure causes the fit point of the device to slide down the stake, which forces the nail head to climb the gentle outward curve on the external surface of the claw ledge. This ensures that the nail will not be bent during the exaction process since the orientation of the extraction force exerted on the nail head by the device remains essentially normal to the stake and parallel with the centerline of the nail.
When the handle has been swung into a vertical position the nail will be completely pulled out of the form board but will still be resting loosely inside the pre-drilled hole through the stake. The operator will then simply move the device away from the stake, carrying the nail with it, to complete the nail extraction operation. Thus, the entire process of pulling the nail is accomplished in one fluid motion with the operator remaining in an upright position, greatly increasing worker comfort and efficiency.